Electronic null indicator for electromagnetic micrometers



2 Sheets-Sheet 1 SE. DAWSON ET AL Filed May 25, 1944 N 'I NVENTOR5.

Samuel E dward Dawson ATTORNEY.

John Rex Pin'rluTE' 3 Mn zwl ELECTRONIC NULL INDICATOR FOR ELECTROMAGNETIC MICROMETERS Feb. 5, 1946.

Feb. 5, 1946.

s. E. DAWSON ET AL 2,393,977

ELECTRONIC NULL INDICATOR FOB ELECTROMAGNETIC MICROMETERS Filed May 25, 1944 2 Sheets-Sheet 2 SHAFT I I*IDI CA'E'OFRZl BALANCE I n I n5 l o BALANCE BQLANOE CONTROL 1 I I: I I I47.

' INVENTORS.

S amuel Edward D awsnfl. B John REX P-lmlufl' ATTORNEY.

Patented Feb. 5, :1946

ELECTRONIC NULL iINDICATOR FOR ELEC- TROMAGNETIC MI CROMETERS Samuel Edward Dawson, Fairway Hills, Md., and

John Rex Pimlott. Lubbock, Tex.

Application May 25, 1944, Serial No. 537,306

(Granted under the act of March 3, 1883, as

' amended April 30, 1928; 370 0. G. 757) 3 Claims.

The invention relates to improvements in measuring apparatus particularly adapted but not necessarily limited to use in measuring shaft torque during transmission of power.

An important object of the invention is the provision of a simple, compact electronic null indicator for manually balanced, alternating current electromagnetic,torsionmeters of the type disclosed in British Patent No. 215,986 granted to Ford.

Another object of the invention is to provide an indicator of the character described having means for indicating slowly or rapidly varying transient torque by the use of a suitable oscillograph.

1 A further object isthe provision of a null indicating device which is adjustable to insure that any indications on either side of the null or zero position will be accurately proportional to the changes in torque being measured. 1

The invention also aims to provide a torsionmeter of the character described having means facilitating the accurate adjustment of its parts of th electromagnetic transmitter. assembly applied to a shaft.

Figure 3 is a fragmentary cross sectional detail view taken substantially on the line 3-3 of Figure 2.

Figure 4 is a diagrammatic view showing the phase relationship of voltages present in various portions of the torsionmeter for one condition of unbalance.

Figure 5 is a front elevational view of the Ford torsionmeter box containing the improved null v indicator.

In the drawings, which show, preferred and modified forms of the invention, and wherein similar reference characters denote corresponding parts throughout the several views, the letter A generally designates the torsionmeter, B-the transmitter assembly, C the receiver assembly, and D the electronic null indicator.

Referring first to the transmitter assembly B, shovm in Figures 1, 2 and 3, there is disposecLin outwardly spaced coaxial relation to the drive to compensate for various irregularities in the electrical characteristics thereof, thus making permissible the slight irregularities in power factor usually found in commercially wound coils used in electromagnetic bridges and correcting for changes in transconductance andtransconductance ratios in commercially manufactured electron discharge devices.

The invention'further aims to provide a nullput position may correspond to any desired condition of shaft. torque. 7

Other objects and advantages of the invention will become apparent during the course of the following detailed description, taken in connection with the accompanying drawings, forming a part-of this specification, and in which-drawings:

Figure 1 is a diagrammatic view of the torsionmeter parts and electrical connections therefor. Figure 1a is a fragmentary diagrammatic view of a modified portion of the torsionmeter.

Figure 2 is a fragmentary side elevational .view 55 shaft IS, a sleeve or husk l6 provided at one end with an internal flange ll disposed in encircling engagement with the driveshaft, as shown in Figure 2. This flange I1 is fastened to the driveshaft, as by setscrew I8. Rigidly secured, .as by screws i9, to an out-turned flange 20 at the opposite end of the husk I6 is a bracket 2| carrying spaced electromagnetic transformers. One of these transformers 22 includes a core 23 carrying primary and secondary windings 24, 25. The other transformer 26 is similar and includes a core 21, and primary and secondary windings 28, 29. As shown in Figure 1, the primary windings 24, 28 are series additively connected and the secondary windings 25, 29 are series differentially connected so that the transformers 22, 26 work in opposition. Suitable slip rings 3l-'-34 cooperate with brushes 35-38 in the usual manner to maintain electrical connections between moving and stationary parts.

Fastened on the drive shaft, as by setscrew 40,

is an annular plate 4| provided with a bracket 42' carrying a screw 43 in threaded engagement with 4| and husk l6 may each be formed in halves separately secured together as by screw 49, 50 respectively, so as' to facilitatev the assembly and dismantling of parts on the shaft l5.

Referring now more particularly to Figure 5, the receiver assembly shown therein includes a rectangular frame 55 supported for movement transversely of the meter box 08, as by leaf spring 51, and bracket 58. Fastened in adjustably spaced relation on the frame 55, as by screws 59, are electromagnetictransformers,

primary and secondary windings 62, 63, the com panion transformer 64 likewise including a core 65 and primary and secondarywindings :60, I].

Fixed to the meter box 56 between the trans- One of thesetransformers includes-acorn SI carrying- '92 through atransformer I I0. Alternating current from the source 92 ,is supplied to the electron discharge devices I01, I02 through a common cathodebias resistor I II and parallel anode reformers 60, 64,. as byscrews 68, is an H-shaped armature '69 cooperating with the transformer cores GI, 65 to'form by gaps 10-13.

- Means-I5 is provided for manually adjusting the frame '55 relative to the armjaturejti and for indicating themagnitude and-sense of displacement 7 of the armature 69 relative to, .the transformers 80, 54 carried by the frame. 'Swivell'ed at I8 tothe frame liis a shaft '11 extending through and in screw-threaded engagement with a stationary bracket 18. Releasabl secured againstrotation on the shaft 11, as by lock-nut I9, is a drum 80 provided with suitable circumferentially extending indicia 8| originating at a central zero mark 82.v Fixed on the frame 55 is an index pointer 83 cooperating with the indicia 8| to indicate the magnitude and sense of any lateral displacement of the transformers 60, t4 relative to the armature 69 by the magnitude and direction of angular displacement of the drum 80. Secured to a knob 84 is a rotary shaft 86 extending into the meter'box and-provided with an arm 86 havmagnetic circuits interrupted sistors H2, H3. Connected between the anode resistors H2, H3 i a balancing resistor I4 pro- .vided with a movable tap- I I5 for adiustably dividing the anodecurrent to compensate for inequalities in resistors H2, H3 and for variations insteadyrstate amplification.

- Means'is provided for impressing, on thecontrollelectrodes I01, I08, alternating signal voltages of opposite polarity and of a magnitude and phase'depending-on the magnitude and phase of ing a forked end 81 in motion transmitting engagement with apin 88 on the drum.

- Turning now toFigure 1, it will be seenthat the series additiveiy connected primary windings 82, 66 of thereceiver assembly 0 and the series additively connected primary windings 2d, 2d of the transmitter assembly B j are connected through conductors 09, 90 and a resistor M to a source 92 of alternating current of any desired frequency. Since 110 volts, 60 cycle supply is'generally the most readily available and is also sum= ciently high in frequency to measure most super= imposed transient-torques, it should be used in all but the most extraordinary cases. The pres ent'invention does not-require the use of voltage regulators, oscillators or electronic apparatus,

other than a twin triode tube to be subsequently described, when it is not necessary that the unbalance of the electromagnetic transformer systems be used to determine torque changes quantitatively. In the majority of torsionmeter applications, the average torque is all that is desired and the transformer systems will. be balanced manually, asby the means it.

- The secondary windings 25, 2d of the transmitter assembly B and the secondary windings $3, 61 of thereceiver assembly 0 are differentially serially connected so that the voltages therein will depend on the relative lengths of the transmitter gaps 45-48 and the receiver gaps iii-it.

respect to the receiver transformers is to be determined, a switch 93 is provided for establishing 'ments of either armature the combined, output of the secondaries of the transmitter and receiver transformers 22, 20, 00, 66. The transformer secondary windings 25, 28, 03; 81 are connected, as. by conductors H6, Hi to the primary winding IIO of a coupling transformer Ila, having the extremities of its second.-

ary winding I 20 connected, as by a double pole switch I2I, respectively to the control electrodes "H.108.- Connected across the extremities of the secondary winding I20 is a voltage divider I22 comprising low impedance resistors I23, I24 and an intermediate balancing resistor I20 having an adjustable tap I20. This resistor I25 constitutes means for dividing the signal voltages between the control electrodes I01, I08 so that, without regard to lack of symmetry in the transmitter and receiver assemblies B, C, or to inequality of transconductance of the electron discharge devices IOI, E02, the galvaxiometer to be hereinafter mentioned, can be made to swing equal distances either side of its zero center for equal movedd, from the balanced position.

The tap I26 is connected, through a condenser I21 and the cathode bias resistor Iii, to the cathodes I05, I06; serially connected between the control electrodes 50?, I00 and a point Iiifi which is intermediate the resistor iii and condenser I21, are grid leak resistors 825, I30 and grid filter resistors iti, I02 respectively. Suit-= able grid filter condensers I33, 88% are disposed between the cathodes I05, its and points ltd, use intermediate the filter and leak resistors, re-

I spectively.

' Thus the differential output or resultant voltage Connectedacross the anode resistors iii, 3, lid is a sensitivity control resistor are provided with an adjustable tap its. serially connected between one extremity I 30 of the resistor and the tap I89 are a center zero galvanometer Ii and a resistor I62.

When it is desired to measure transient or,

oscillating torque, a cathode ray oscillograph I03 may be connected across the resistor I38 at socket I05. During use of the osciilograph I43, it is preferred to limit current flow resulting from unbalanced signal voltages. Because of the high 1 input impedance of the electron tube I00, it is only necessary to-eliminategthe coupling transformer Ht and connect the, transmitter and receiv'er output conductors He, II] directly to the control electrodes I01, I00 to prevent appreci- 1 able current flow for maximum unbalance and hence to eliminate the principal cause of errors .zero. g the lock-nut 19 and set so that the index 83 will correspond to drum scale zero. This adjustment correlates the zero setting of the drum scale with 2,893,977 due to the use of non-null methods of making electrical measurements through slip rings and over transmission lines of variable length. In connecting the conductors H8, H1 directly to the control electrodes I01, I08, the coupling transformer H9 shown in Figure l is omitted, as indicated in Figure la, and a voltage divider I 22a is employed having resistors I23a, I24aof higher impedance than the corresponding resistors I23, I24 of Figure 1. If it is desired to measure small superimposed transient or oscillating torques while the instrument is used as a null indicator for average torque measurements, the arrangement shownin Figure 1 will be used, except that the galvano meter filter condenser I45 will be disconnected as by opening, a switch I46. The adjustable contact I39 of the-resistor sembly. Since the transformer windings are connected in opposition, any displacement of the transmitter armature 44 in one direction from its position of balance will cause a signal voltage to I38 should be left'in position for zero sensitivity the primary windings 24, 28, 82, 60 by the alternating current source 92.

The signal voltage I 52 impressed on the control electrode I01 originates in the secondary winding I of the coupling transformer and is assumed to be in phase with the reference voltage ISI for the selected condibefore use will now be described. First the sys-' tem isenergized for a warming-up period, as by closing a suitable switch I41 and the sensitivity control tap I39 is moved to its position of full sensitivity. With the switch m open, the bal- I ance control resistor I I4 is adjusted at the tap II5 until the galvanometer I4I reads zero. This adjustment compensates for inequalities in the anode resistors H2, H3 and for variations in steady state amplification such as produced by inequalities in resistors I29, I or in the charuntil the pointer will indicate zero with the sensitivity control in any position. Then the switches I2I and 93 are closed and the knob 84, shown in Figure 5, is turned until the galvanometer reads j The drum 80 should now be released at the neutral position of the armature 69. Next the equalizing balance control tap I26, is adjusted until the galvanometer pointer swings equidistantly each side of its zero position upon rotation of the drum equiangularly'each side of drum scale zero. With the switch 83 open, the relationship of the transmitter armature 44 and transformers 22, .28 is adjusted at screw 43 'until the galvanometer again reads zero with the drum scale at zero. When the system has been correctly balanced, the galvanometer will not deflect upon closing and opening the switch 83.,

tion of unbalance. Thus the signal voltage I53 impressed on the control electrode I08 is 180 degrees out of phase with the reference voltage I5I. The resulting increase in current flow through the space discharge device IN and decrease in current flow through the space discharge device I02 gives rise to a decreased voltage level I54 at the anode I03 and an increased voltage level I55 at the anode I04. The voltage difference I58 between these voltage levels I54, I55 'is impressed on the sensitivity control resistor I so that the resistance drop through the section thereof included in the galvanometer circuit will deflect the galvanometer in a direction and magnitude depending on the direction and magnitude of the condition of unbalance. If new the armature 89 is moved, as by rotation of knob 84, in such a direction as to cause the galvanometer needle. to return to zero and this motion is continued beyond the balance point, the galvanometer needle will swing in the opposite direction. It will thus be seen that we have provided an improved measuring apparatus fulfilling th'e requirements of simplicity, directionality, accuracy and ease of installation and adjustment.

scope of the following claims. i

The invention described herein may be manufactured and'used by or for. the Government of the United States of America for governmental I purposes without the payment of any royalties thereon or therefor.

We claim: 1. 'In measuring apparatus of the. class described, a source of alternating current; a trans-- mitter assembly; a receiver assembly; said assemblies each including electro-magnetic transform.-

' ers energized by said alternating current source and working in opposition, an armature having a I neutral position relative to said transformers, the

j outputs of said transformers being balanced upon discussed in connection with one condition of unbalance in the transmitter assembly B produced by displacement of the armature from its neutral position in a direction depending on the direction of rotation of the shaft. Obviously, the armature 89 must be moved in the correct direction to cause the unbalance. in the receiver 1 assembly secondary coils 83, -81-to he q al and disposition of said armature in said neutral -po-' sitiom said armature being displaceable in either displacement of the armature in one sense from saidineutrai position to the phase upon displacement of the armature in the other sense; means dlsplacingthetransmittermarmature from its ,4 condition to be measured; means indicating the 1 :amount' and sense of displacement. ii any, of the receiver armature from its neutral position; two

ode, aicathodeand a control-electrode; means including a coupling transformer '5 energized by t 1 the-diilerential' output. of saidntransmitter "and receiver assemblies for: impressing equal signal v blies are unbalanced, the magnitude and phase of said-voltages depending on the amount and sense' 1 'o'ixunbalance of said assemblies; anode-cathode 1 a 'circuits ior said dis'chargefdevice'g including'relatively: adjustable resistors;- "means'ior supplying:

:5 saidclrcuitswith-alternating current in synchroelectron dischargedevices each including an anvoltages or opposite polarity onxthe' control electrodes of said discharge device when said assemsource; means indicating the magnitude and direction of any diflerence in current iiow through said circuits; and a switch. operable to eliminate any effect of said transmitter output on said signal voltages so thatthe neutral position oi the receiver armature with respect to the receiver transformers may be indicated by said last-mentioned indicating means.

3. In measuring apparatus 01 the classde scribed, a source of alternating current; atransmltter assembly; a receiver assembly; said assemblies eachincluding electro-magnetic transformers energized by said: alternating current source andworking in opposition,- an armature having a neutral position relatlve'to sa'ld transformers, the outputsj'of said transformers being nism' with the alternatingcurrent 'from said 1 source; and means indicating the magnitude: and

' balanced iupon disposition. of saidarmature in 1 said neutral position',,said armature being disdirection of any diiiererice in current flow I through said circuits including a center-zero gal-,

vanometer serially connected withsaid resistors;

switch" for disconnecting said coupling trans- !ormer from said control electrodes whereby-said galvanometer may be balanced with respect to said dis'charge 'devices uninfiuenced by said signal voltages by adjustment of sald resistors with aid switch inits open position. t

2. In measuring apparatus of the class described; a-source of alternating current; a transmitter assembly; .a'receiver assembly; said assemblies each including electromagnetic trans iormer's energized by said, alternating current sources. and working in opposition, an armature having a neutral position relativevto said transformers, the outputs of said transformersbeing balanced upon dlspositionfof said armature in saidneu'tral position, said armature being displaceable in either'oi two-opposed senses from said neutral position to disturb the balance of said transformer outputs whereby a diflerential output is produced, the magnitude of which varies said signal voltage impressing means including a placeable in eitherrortwo opposed senses from i said neutral position to disturb the balance of said transformer outputs whereby a differential output is produced, the magnitude or which varies with the displacement and the phase of which is opposite upon displacementof the armature, in one sense from said neutral position to the phase upon displacement of the armature in the other sense; means displacing thetransmitter armature-from its neutral position in an amount and sense depending on the magnitude with the displacement and the phase of which is opposite upon displacement of the armature in one sense from said neutral position to the phase upon displacement of the armature in the other sense; means displacing the transmitter armature from its neutral'position 'inan amount and sense depending on the magnitude and sense of a force or condition to be measured; means indicating the amount and' sense of displacement,

. if any, ofthereceiver armature from its neutral position; two electron discharge-i devicesqeach V-in- V eluding ananode; a-- cathode and 'acontrol =elec- -trode; means energized by the diilerentialoui put pi said transmitter and receiver: assemblies and sense of a forceor condition to be. measured; means indicating the amount and sense of displacement. if any, of the receiver armature from its neutral position; two electron dischar e devices each including an anode, a cathode and a control electrode; means for impressing equal signal voltages of opposite polarity on the control electrodes, of said discharge deviceswhen said assemblies are unbalanced, the magnitude and phase of said voltages depending on the amount and sense of unbalance of said assemblies, said voltage impressing means-including a coupling transformer normally energized by the differential output of said transmitter and receiver assemblies, a resistor connected between said control electrodes and across the output of said coupling transformer, and means connecting the cathodesof said discharge devices to any one of a plurality oi'points along the resistor for adJustably dividingv the signal voltages impressed on the control electrodes to balance the outputs of said dischargedevices; anode cathode circuits for said discharge. devices; meansforsupplying W said circuits with alternating current in synchronism'with the alternating current from said I source; means indicating the magnitudeand direction of any diflerence in'current flow through for impressing equal signal: voltagesof opposite 1 charge devices when said'ass'emblies are'unbalpolarity on the control; electrodesfior said dis- 'saidcircuits; and a switch operable to eliminate any eflect of{ said transmitterv output on said 1 signal voltages so that the neutral position of the receiver armature with respect'to 'the receiver 1 transformers may beindicated by'said' last-mentioned indicating means.

SAMUEL EDWARD DAWSON.

com: REX PIMLO'IT. 

